Anti-glare sheet for image display device

ABSTRACT

An anti-glare sheet that exhibits excellent glossy black textures, blackness in dark locations, and anti-glare properties for dynamic images, and that is suited to the implementation of high quality images. The anti-glare sheet has, on at least one surface of a transparent substrate, an anti-glare layer comprising binder resin, diffusion particles, and binder particulates. The transmission intensities of the anti-glare sheet satisfy specific relational equations.

TECHNICAL FIELD

The present invention relates to an anti-glare sheet for an image display device that has excellent vivid complexion and blackness, blackness in dark surroundings and an excellent antiglare property for dynamic image purposes (antiglare property for dynamic images), and that is suitable for achieving high image quality.

BACKGROUND ART

In image display devices such as cathode ray tube (CRT) displays, liquid crystal displays (LCD), plasma displays (PDP) and electroluminescence displays (ELD), the outermost surfaces are generally provided with optical laminates for anti-reflection. Such optical laminates for anti-reflection minimize virtual image formation and reduce reflectance by diffusion and interference of light.

One type of known optical laminate for anti-reflection is an antiglare film having an irregularly shaped antiglare layer formed on the surface of a transparent base material. The antiglare film can diffuse external light and prevent reduction in visibility caused by external light reflection or virtual image formation, by the irregular shape of the surface.

An example of a known conventional antiglare film is one wherein a resin containing a filler such as silicon dioxide (silica) is coated on the surface of a transparent base material film to form an antiglare layer (see PTLs 1 and 2, for example).

Such antiglare films include types in which irregular shapes are formed on the surface of the antiglare layer by aggregation of particles such as cohesive silica, types in which an organic filler is added to the resin to form irregular shapes on the layer surface, and types in which a film having irregularities on the layer surface is laminated to transfer the irregular shapes.

All such types of conventional antiglare films are designed to produce a light diffusing and antiglare effect by the action of the surface form of the antiglare layer, and require larger and a greater number of irregular shapes to increase the antiglare property, but when the irregularities or their number are increased, this raises the haze value of the coating film, causing discoloration and concomitantly lowering the contrast.

As the opportunity to view displays with high image quality movies and the like have increased in homes as well, there is increased demand for blackness of black screens in dark rooms (hereunder referred to as “blackness in dark surroundings”).

The haze exhibited by surface irregularities is defined as the “surface haze” while the haze exhibited when smoothing has been performed using a resin that forms surface irregularities, or a resin with a difference in refractive index of at least 0.02 from such a resin, is defined as the “internal haze”, and these are measured according to JIS K 7136 (2000).

The haze value, or the ratio of the internal haze and total haze, is commonly used as a simple method for evaluating contrast. Specifically, it has been considered that an optical sheet with low contrast reduction can be produced by specifying the materials and controlling the production conditions in the optical sheet production process, in order to control the haze value (see PTLs 1 to 3).

However, contrast can differ even with the same haze value, and even with production using the haze value and the ratio of the internal haze and total haze as indexes, for example, it is not always possible to stably obtain a satisfactory antiglare sheet for an image display device.

In addition, it has been attempted to lower the reflectance by additionally providing a low-refraction light interference layer on the antiglare layer, but this requires precise formation of a film of about 100 nm, and is extremely expensive.

Furthermore, in recent years a variety of different kinds of viewing environments have appeared due to the diffusion and wider evolution of various types of delivery systems including one-seg, and the performance required for antiglare sheets has become ever more wide-ranging and personalized.

For example, with increasing opportunities for movie appreciation and the like, there is increasing demand for reproduction of dynamic images with high image quality in dark rooms, in order to experience a high-level viewing environment equivalent to that of a movie theatre, while as mobile usage continues to increase, there is also demand for image quality with physical strength and satisfactory balance between dynamic images and still images in light rooms, in order to bring out still images and dynamic images in the bright outdoors.

In other words, the image quality required for display terminals varies, and it is desired to develop an antiglare sheet for an image display device having performance suitable for the viewing environment.

PTL 4 and 5 indicate examples where the requirements differ depending on the viewing environment, and teach that still images and dynamic images have different requirements for performance, as well as different viewing conditions by observers.

As a result of diligent research on the problems described above, the present inventors have found that the sum of the internal diffusion and surface diffusion alone that has been considered in the prior art does not account for the total haze, but that in addition to the internal diffusion and surface diffusion, the total haze is also affected by the positional relationship between the diffusion particles and the surface irregularities.

The present inventors have also found, as a result of conducting diligent research on the performance required by antiglare sheets for image display devices suited both for high blackness in dark rooms and in light rooms and for high-level dynamic images and still images, such as for liquid crystal display devices (hereunder these will also be referred to simply as “for liquid crystal display devices”), and that in order to obtain a high level of blackness in dark rooms it is necessary to exhibit diffusion properties of a nature such that virtually no “stray light component” is produced, a factor that has not been considered in the past. The term “stray light component” refers to any of the uncontrollable light components traveling in directions inside the antiglare sheet different from the intended direction, among light impinging into the interior of the antiglare sheet, due to diffusion factors present on the surface of and/or inside the antiglare sheet (for example, on the surface they are the irregular shapes themselves, or in the interior, they are diffusion factors such as the particles used to form the irregular shapes), and they are usually reflected repeatedly inside the antiglare sheet.

It was also found that in order to obtain satisfactory image quality for viewing, it is important to sufficiently provide the regular reflection component of external light, which in the past has only been an object of prevention, while also considering the stray light components of projected light for dynamic images and still images in a light room.

In other words, in regard to the stray light components, when dark sections (for example, black) and light sections (for example, white) are present in the same screen, projected light in the light sections partially presents as stray light due to diffusion factors in the optical sheet, not only producing “flares”, or light emitted from dark sections, and lowering contrast, and especially reducing dark room contrast, but also causing loss of stereoscopic quality and resulting in images with poor planar variation.

The stray light component has minimal influence when viewing from the front, and tends to have a stronger influence when viewing from oblique directions.

In regard to the regular reflection component of external light, it was found that an optical film with extremely low regular reflection causes images to be perceived as simulated images, being subject to human sensory characteristics, whereas an optical film with an appropriate regular reflection component presents clear images and tends to result in their perception as actual objects, increasing the unique gloss and luminance of images on a dynamic image screen, to produce images with a sense of motion.

Such performance that includes contrast, a stereoscopic visual effect and sense of motion, that are required for such dynamic images (for example, for a scene with a youth under a blue sky, the black hair displayed on the screen is smooth black, the black pupils are moist black, and the skin is visible with the vivid brilliance characteristic of youth) will be referred to as “vivid complexion and blackness”.

In addition, for film viewing under illumination, or for mobile purposes, a property of preventing unwanted reflection (an antiglare property) is desired even for viewing of dynamic images. An “antiglare property for dynamic images” is a property that is not completely free of virtual images of objects in front of the image display device, but rather slightly prevents unwanted reflection, where the outlines and borderlines of objects on borders and backgrounds are slightly halated for an observer observing the dynamic images.

Moreover, in recent years, there is a demand for antiglare sheets for liquid crystal display devices with excellent “blackness in dark surroundings”, which is a degree of notable, high-level blackness under high-level viewing conditions, such as for film appreciation, or in other words, viewing under dark room conditions without external light, and in the optimal range of the display device (a viewing range that allows viewing with a front luminance of 33.3% or greater).

Still images must have excellent contrast and greater prevention of unwanted reflection, and such performance of contrast and prevention of unwanted reflection required for still images will be referred to as “image crispness”.

In other words, there is an increased preference that antiglare sheets for liquid crystal display devices should have excellent vivid complexion and blackness and image crispness.

Evaluation of image quality has included the “black tightness” mentioned in PTL 6 and “glazed black feel”, mentioned in PTL 7.

In order to improve narrowness of angle, which is a fundamental defect in liquid crystal displays, antiglare sheets are often provided with diffusibility. However, providing diffusibility can lower contrast, especially for frontal viewing.

Black tightness is evaluated as a compromise between viewing angle enlargement and contrast, and by comparing blackness during power-off and blackness during power-on (black images) when viewing directly from the front of the display, with a more intense blackness being evaluated as a more powerful tight feel for the screen.

In addition to stray light components that are very weak in the front and more noticeable at greater oblique angles, in a liquid crystal display system structure the light leaking from the liquid crystal display unit itself (leaked light) is present even during black display, and therefore the blackness during power-on, as seen directly from the front, is the level of blackness resulting from a combination of this leaked light and external light reflection, while blackness during power-off is the blackness with only external light reflection, since no projected light is present.

Stated differently, “black tightness” means an intense level of blackness against both external light and leaked light, without considering the stray light components, unlike the aforementioned vivid complexion and blackness, and also without consideration of an appropriate necessary level for the regular reflection component, and therefore even if the contrast is high, the gloss and luminance of the image is inferior, no sense of motion is produced, and the vivid complexion and blackness is not increased. In particular, since increasing diffusion and widening the viewing angle are a priority, stray light components are easily produced and the blackness in dark surroundings tends to be reduced.

Furthermore, a “glazed black feel” is black reproducibility when an image display device displays black in a light room environment, i.e., abundant expression of graded black, by minimizing diffusion of the non-regular reflected light component of light incident to the optical laminate from the exterior, preventing non-regular reflected light from reaching the eye of the observer, and visual evaluation is made under three band fluorescence, after attachment to a cross nicol polarizing plate or a black acrylic board via an acrylic pressure-sensitive adhesive for optical films (product with total light transmittance: ≧90%, haze: ≦0.5%, film thickness: 10 to 55 μm, such as the MHM Series by Nichiei Kakoh Co., Ltd., or trade name: “L8010” by Hitachi Chemical Co., Ltd.) on the side opposite the film side of an optical laminate.

That is, with this measurement method, evaluation of dynamic images is not performed and the effect of stray projected light components is completely ignored. Therefore, even with high gloss and luminance, no dark room contrast or stereoscopic visual effect is produced, and the vivid complexion and blackness is not increased.

“Contrast” is the ratio of white luminance to black luminance, and since the absolute value of black luminance is much smaller than the white luminance, the effect of black luminance on contrast is greater. In order to obtain images with excellent contrast, it is necessary to have excellent “black tightness”, as light room blackness for a wide viewing angle, “blackness in dark surroundings” as the absolute blackness, and “glazed black feel” as abundant graded expression in the black region.

Also, in order to present both still images and dynamic images, it is necessary to exhibit excellence at least in terms of vivid complexion and blackness with a stereoscopic visual effect and sense of motion.

In PTLs 8 and 9, which limit the diffusion property of antiglare sheets, the contrast is satisfactory, but no consideration is given to the issues of physical performance including adhesiveness and hard coat properties, which are indispensable for practical use, or glare and presentation of both dynamic images and still images, and therefore sufficient performance has not been exhibited.

CITATION LIST Patent Literature

-   PTL 1: Japanese Unexamined Patent Application Publication No.     2002-267818 -   PTL 2: Japanese Unexamined Patent Application Publication No.     2007-334294 -   PTL 3: Japanese Unexamined Patent Application Publication No.     2007-17626 -   PTL 4: Japanese Unexamined Patent Application Publication No.     2006-81089 -   PTL 5: Japanese Unexamined Patent Application Publication No.     2006-189658 -   PTL 6: Japanese Unexamined Patent Application Publication No.     2007-264113 -   PTL 7: Japanese Unexamined Patent Application Publication No.     2008-32845 -   PTL 8: Japanese Unexamined Patent Application Publication No.     2010-60924 -   PTL 9: Japanese Unexamined Patent Application Publication No.     2010-60925

SUMMARY OF INVENTION Technical Problem

In light of this situation, it is an object of the present invention to provide an antiglare sheet for an image display device such as a cathode ray tube (CRT) display, liquid crystal display (LCD), plasma display (PDP), electroluminescence display (ELD) or the like, that does not employ a low refraction interference layer, that in particular has excellent high-level blackness (blackness in dark surroundings), vivid complexion and blackness and a glazed black feel in dark surroundings, that has an antiglare property (an antiglare property for dynamic images) tolerable for dynamic image purposes, and that is suitable for practical use.

Solution to Problem

A trade-off exists between viewing angle and image quality in liquid crystal displays, for example. In the past, liquid crystal television sets have had a narrow viewing angle, which has been considered a drawback from the viewpoint of substitution for isotropic CRTs, and larger viewing angles have also been desired for antiglare sheets.

However, the present inventors investigated the techniques described below, based on the idea of liquid crystal televisions as new displays and considering changes in viewing environments, without considering narrowness of viewing angle and isotropy as drawbacks, but with emphasis on frontal image quality, in order to be free from the restriction of having to achieve trade-off between viewing angle and image quality.

Contrast and antiglare properties have hitherto been considered to depend on surface form, which includes the arithmetic mean roughness (Ra), ten-point height of irregularities (Rz) and average spacing of surface irregularities (Sm), based on JIS B-0601-1994 which deals with surface irregularities, and the mean inclination angle of irregularities (θa), based on the definition described in the instruction manual of the surface roughness measuring instrument SE-3400 by Kosaka Laboratory, Ltd. (Revision Jul. 20, 1995)), or have been considered to depend on the state of reflection of external light that is based on the difference in refractive index between the interior dispersing agent and binder resin, or the shapes of internal diffusion particles. In other words, the effect of interaction between surface irregularities and internal diffusion factors has not been considered.

The definition for calculating θa will now be explained.

In an irregular shape existing within a range of reference length L, heights are present at the highest parts from one raised section to the next raised section, and recesses are present at either end. The positions of the recesses are not necessarily at the same height.

The heights from each recess position to the triangular tip are designated as h1 and h2. Similarly, when the heights of all of the raised sections in the reference length range are measured from the recesses to the tips (each raised section having two heights), and the sum of the heights is determined, calculation of the arctangent of the value divided by the reference length L yields the angle. θa=tan⁻¹[(h1+h2+h3+h4+ . . . +hn)/L]

The present inventors have found that the diffusion properties are significantly different for light passing through the diffusion particles and for reflected light, from projected light incident to the diffusion particles and external light, due to the difference in refractive indexes of the internal diffusion particles and binder resin, as shown in FIGS. 8-1 to 8-4, and that a larger difference in refractive index between the diffusion particles and binder resin increases the amount of light reflected by the diffusion particles and increases the diffusion angle of light passing through the diffusion particles, such that generation of stray light components due to projected light increases, the amount of light reflected from external light increases, and the contrast is lowered.

It was further found that, in regard to projected light as shown by 1-1 to 1-5 in FIG. 7-1, the transmission and reflectance properties of projected light passing through the diffusion particles, as well as generation of stray light components that impair resolution and contrast, differ significantly depending on the positional relationship between the diffusion particles and surface irregularities, and also that in regard to external light as well, as shown by 2-1 to 2-4 in FIG. 7-2, the generation of stray light components that impair the reflectance properties and contrast of light reflected by the diffusion particles, from external light incident to the diffusion layer interior, differs significantly depending on the positional relationship between the diffusion particles and surface irregularities, and by also considering the shapes of surface irregularities, the diffusion particle properties and the relationship between the surface irregularities and internal diffusion particles in an antiglare sheet for a liquid crystal display device according to the present application, it was possible to obtain an antiglare sheet for a liquid crystal display device having not only excellent contrast and antiglare properties for dynamic images, but also vivid complexion and blackness (for dynamic images) and image crispness (for still images).

Also, when the positional relationship between the surface irregularities and diffusion particles is such that the diffusion of external light reflected by the diffusion particles is large, as shown by the diffusion particle 2-2 in FIG. 7-2, the diffusion of projected light is also large tending to produce stray light components, as indicated by 1-2 in FIG. 7-1, thus also tending to result in contrast reduction due to the projected light.

That is, the magnitude relationship for contrast reduction by stray light components from projected light can be considered to approximate the reflectance properties for external light. The same applies for vivid complexion and blackness (for dynamic images) due to stray light components. Also, this stray light component generation is increased in the conventional methods that emphasize viewing angle, wherein LCD leaked light is widely diffused by providing wide-angle diffusion, even with low antiglare layer strength, and they have lacked a high level of blackness and in dark rooms, and blackness in dark surroundings.

In other words, it is not possible to obtain an excellent antiglare sheet even by controlling the diffusion properties such as total haze or internal haze, or by controlling the surface form including the arithmetic mean roughness (Ra), ten-point height of irregularities (Rz), average spacing of surface irregularities (Sm) and mean inclination angle (θa), as in the prior art.

The present inventors have found that, in order to obtain dynamic images with excellent vivid complexion and blackness, it is satisfactory to have a state of high directivity of projected light from the interior (a state where light is concentrated in a certain direction), i.e. it is satisfactory for the antiglare sheet for a liquid crystal display device to have preferably low transmission scattering and high regular transmission intensity, and to minimally reduce the stray light component of external light and projected light.

On the other hand, high transmission scattering generates stray light components and lowers the directivity of internal projected light (a state in which light diffuses and does not concentrate with directionality) and causes images to appear discolored, such that vivid brilliance for display of flesh colors is not obtained.

To obtain still images with excellent image crispness, however, it is necessary to achieve both contrast and prevention of unwanted reflection. However, when the antiglare property is increased to improve prevention of unwanted reflection, the reflected scattering increases, contrast is reduced and image crispness is impaired.

As a result of much diligent research on image crispness (still images), the present inventors have found that virtual images become a problem for an observer because the focus of the observer, when viewing a still image, repeatedly meets at some images present on the exterior, that have been reflected on the outermost surface of the image display device (for example, the image of the observer or reflected images of objects in the background), and the focus fails to settle on the original image.

As a result of further research, it was found that if the outlines of a reflected external image that is reflected during viewing of a still image are rendered indistinct, the virtual image is no longer a problem and contrast reduction can also be minimized, while resulting in improved image crispness.

Incidentally, the “antiglare property for dynamic images” is weak prevention of unwanted reflection, limited to viewing of dynamic images. The perception of reflection with still images is greater than with dynamic images, and requires stronger prevention of unwanted reflection than for dynamic images. In other words, so long as image crispness is satisfied, the antiglare property for dynamic images will be simultaneously satisfied.

If the subject is limited to dynamic image viewing, however, it is sufficient to satisfy the antiglare property for dynamic images, which is weak prevention of unwanted reflection, even if image crispness is not satisfied for still images.

In other words, in order to achieve both image crispness required for still images and vivid complexion and blackness for dynamic images, it was found that it is important to minimize the reduction in the regular transmission intensity component of transmission scattering, and appropriately ensure low reflected scattering that renders the outlines of reflected external images indistinct, while also reducing the stray light component.

This means that the regular reflection intensity component is converted to diffusion near the regular reflection, and considering (a) to (c) below, it means that an antiglare sheet for a liquid crystal display device can be obtained that exhibits both still image crispness and dynamic image vivid complexion and blackness.

That is, it satisfies the three factors of: (a) low transmission scattering (high regular transmission intensity component), (b) a small regular reflection intensity component, and (c) conversion to diffusion near the regular reflection.

An antiglare sheet usually includes added conductive particles to impart an antistatic function or added fine particles to prevent glare or form surface irregularities, and it has internal diffusion other than the diffusion by the surface irregularities (hereunder referred to as “external diffusion”).

FIG. 1 shows the results of a simulation of surface reflectance of a resin coating film with a refractive index of 1.50, and reflectance on the surfaces of spherical dispersing agent particles dispersed in the resin coating film, with varying particle refractive indexes. As shown in FIG. 1, the reflection intensity by internal diffusion factors is significantly smaller than the reflection intensity by external diffusion, and therefore surface diffusion is the dominant factor of the diffuse reflection intensity.

Also, diffusion of transmitted light by the surface form is n×sin θ=sin φ based on Snell's law, where φ is the emergence angle from the slanted surface at φ and n is the refractive index of the coating film, and the emergence angle ψ is arcsin(n×sin θ)−θ.

Reflection, on the other hand, undergoes twice the change in the slanted surface at θ, based on the law of reflection, and therefore the angle of reflection φ is 2×θ. Thus, within the ordinary range for coating film refractive indexes and antiglare sheet surface forms, the diffusion angles of reflection and transmission with respect to the surface inclination angle may be considered to be proportional, as shown in FIG. 2 which has the results of calculation for a resin surface with a refractive index of 1.50.

That is, since low regular reflection intensity is low regular transmission intensity, and increasing the diffusion near regular reflection increases the diffusion near regular transmission, all three factors demanded for an antiglare sheet for a liquid crystal display device with both prevention of unwanted reflection for still images and vivid complexion and blackness for dynamic images as described above, can be converted to transmission. Also, as explained above, they can still be converted while satisfying the antiglare property for dynamic images.

That is, factors (a) to (c) can be restated as: (a) low transmission scattering (high regular transmission intensity), (b′) a low regular transmission intensity component, and (c′) conversion to diffusion near regular transmission.

Factors (b′) and (c′) represent a small ratio Q/q between the regular transmission intensity (Q) and diffusion intensity near regular transmission (q), while (a) represents a large Q/q.

Incidentally, since the haze value hitherto used in antiglare sheets for liquid crystal display devices is the ratio of light that has been diffused at least 2.5 degrees from regular transmission with respect to the total light rays, as indicated by JIS K7136 (2000), it is not possible, simply based on the haze value, to imagine using the aforementioned diffusion near regular transmission (especially diffusion of less than 2.5 degrees).

However, since it is impossible to prevent glare with an antiglare sheet for a liquid crystal display device with absolutely no internal diffusion, it is necessary for at least a small degree of internal diffusion to be present. The diffusion size by internal diffusion may be diffusion not exceeding 2.5 degrees, in which case the haze due to internal diffusion is zero.

The diffusion intensity near regular transmission in the case of isotropic diffusion was therefore considered.

As shown schematically in FIG. 3, in regard to the diffusion intensity, when a layer with diffuse transmission intensity distribution b is laminated on a transparent base with diffuse transmission intensity distribution a, the reduction rate of the diffuse transmission intensity is larger closer to 0 degrees, and therefore the reduction is greater with intensity closer to 0 degrees, and the antiglare sheet for a liquid crystal display device has a diffuse transmission intensity distribution of c.

Also, since the internal diffusion factor and external diffusion factor in an antiglare sheet for a liquid crystal display device generally both have sparse distribution, the intensity distribution of the diffusion property is the sum of the diffusion intensity distribution due to the diffusion factors, and the two intensity distributions having only the intensity for regular transmission without the diffusion factors.

As shown in FIG. 4, if the virtual regular transmission intensity U is defined as the intensity for the slopes of the intensity at regular transmission ±1 degree and regular transmission ±2 degree, that have been extrapolated from regular transmission, then U approximates the regular transmission intensity of the diffusion property due to diffusion factors, and Q/U is the ratio of “the portion Q with no diffusion factor” and “the regular transmission intensity U of the diffusion factor portion”, or in other words, the ratio of “the intensity Q of regular transmission without transmission scattering” and “the regular transmission intensity U guided in the direction of 0 degrees by transmission scattering”, i.e. it is a measure of the state of diffusion near regular transmission.

FIG. 3 and FIG. 4 also show that U is larger with greater intensity near regular transmission, and that the change in U with respect to Q is smaller with a greater initial diffusion angle.

Stated differently, using U instead of the intensity q near regular transmission is a form of also incorporating the size of the (a) transmission scattering.

Thus, by limiting the range of Q/U to a specified range, it is possible to achieve a satisfactory balance between image crispness and dynamic image vivid complexion and blackness, to obtain an antiglare sheet for a liquid crystal display device having both of these aspects of performance.

In other words, since in terms of the surface form (external diffusion factor), Q/U is approximately the ratio between the flat section which provides regular transmission and the concavoconvex section which is the non-regular transmission angle, it is related to the irregularity slope angles and the percentage of irregularities, while in terms of internal diffusion it is related to the difference in refractive indexes of the diffusion particles and the binder resin and the probability of collision of diffusion particles and the shape, and in terms of interaction between the surface form and internal diffusion, it is related to how much further the interaction is weakened or strengthened, so that it determines the vivid complexion and blackness (for dynamic images) and quality of image crispness (for still images).

In order to realize a high level of blackness in dark surroundings, however, it is desirable to further prevent stray light, and therefore stray light is further considered.

Generally speaking, at the interface between a layer with refractive index n and air, the proportion of reflection at the interface when light from the layer interior impinges on the interface at angle θ is represented by the following formula, based on calculation according to the law of reflection and Snell's law, where p polarized light is represented as Rp and s polarized light is represented as Rs. Rp=((cos θ−n×cos(arcsin(n×sin θ)))/(cos θ+n×cos(arcsin(n×sin θ))))² Rs=((cos(arcsin(n×sin θ))−n×cos θ)/(cos(arcsin(n×sin θ))+n×cos θ))²

Also, the transmitted scattering angle φ with low internal diffusion in an antiglare layer with surface irregularities is calculated based on Snell's law: φ=arcsin(n _(B)×sine θs)−θs where θs is the inclination angle of surface irregularities and n_(B) is the refractive index of the binder resin.

Thus, when projected light impinging on an antiglare layer from the transparent base material side impinges on an irregular surface with inclination angle θs (the interface between the antiglare layer and air), the relationships θ=θs, n=n_(B) may be assumed for the above formula, and therefore the proportion of reflection on the irregular surface is represented by Rp and Rs, which can be represented as functions of the transmitted scattering angle φ. Also, larger Rp and Rs values correspond to increased stray light components since more light is reflected at the irregular surface and returns into the antiglare layer.

FIG. 6 shows values calculated by the above formula, using a refractive index of 1.50 for a common binder resin. Since the surface irregularities on the antiglare layer are randomly formed, the average reflection proportion can be represented as (Rp+Rs)/2. As clearly seen in FIG. 6, a transmitted scattering angle exceeding 30 degrees results in drastically increased reflection, i.e. drastically increased stray light components.

Thus, transmission scattering at 30 degrees or greater is preferably absent in order to avoid generating stray light components, and since reflection begins to increase from 20 degrees, limiting the transmission scattering to no greater than 20 degrees can reliably prevent generation of stray light components.

In order to realize such optical properties, a solution was found based on the following understanding of the mechanism of irregularity formation on the antiglare layer surface by diffusion particles.

Specifically, the volume of a binder resin shrinks when it is cured. Diffusion particles, on the other hand, do not shrink, and therefore resistance by the diffusion particles to shrinkage of the binder resin results in raised sections on the surface at locations corresponding to the diffusion particles and thus formation of irregularities. Consequently, particularly when diffusion particles are situated near the surface of a binder resin, the raised sections produced by the diffusion particles tend to have steep slopes.

However, the binder fine particles become locally concentrated around the diffusion particles (being much smaller than the diffusion particles they do not act as diffusion factors, but are fine particles that are able to flow together with the binder and thus function as a binder), whereby the binder at those sections (consisting of the binder resin and the binder fine particles) is resistant to cure shrinkage, and as a result the raised sections around the diffusion particles tend to have gentle slopes. In addition, when the diffusion particles are organic fine particles, their difference in specific gravity with the binder resin is small and hence they tend to be located near the binder surface, but when the binder fine particles are inorganic fine particles, the specific gravity is larger than that of the binder resin, creating an effect of submerging the organic fine particles, and thereby resulting in a greater effect of attenuating the slopes of the irregularities.

Thus, it is a feature of the present invention that the ratio Q/U and also Log₁₀(Q₃₀/Q) are targets of focus, but in order to obtain a more excellent effect, it is also possible to achieve the object of the invention by combining other parameters, i.e. the other optional parameters specified in the claims of the invention.

The present invention has been completed based on the knowledge described above, and it encompasses the following modes.

(1) An antiglare sheet having an antiglare layer comprising a binder resin, diffusion particles and binder fine particles on at least one side of a transparent base material, the antiglare layer having irregularities on the side opposite the transparent base material, the irregularities being formed by raised sections, constituted by the diffusion particles and/or the diffusion particle aggregates, that are surrounded by a localization layer with high density of the binder fine particles, wherein the following inequalities (1) and (2) are satisfied, Q representing the luminance in the direction of regular transmission, when visible light rays have been irradiated on the antiglare sheet perpendicular to the transparent base material side, Q₃₀ representing the luminance in a direction 30 degrees from regular transmission, and U representing the mean value of the transmission intensity determined by extrapolation of a straight line connecting the luminance in the direction +2 degrees from regular transmission with the luminance in the direction +1 degree from regular transmission, and a straight line connecting the luminance in the direction −2 degrees from regular transmission with the luminance in the direction −1 degree from regular transmission, to regular transmission. 10<Q/U<36  (Inequality 1) Log₁₀(Q ₃₀ /Q)<−6  (Inequality 2)

(2) The aforementioned antiglare sheet wherein the specific gravity of the binder fine particles is greater than the specific gravity of the binder resin.

(3) The aforementioned antiglare sheet wherein the binder fine particles are hydrophobic-treated fumed silica and/or a laminar inorganic compound.

(4) The aforementioned antiglare sheet satisfying the following (inequality 3), where T (μm) is the thickness of the antiglare layer. 3<T<10  (Inequality 3)

(5) The aforementioned antiglare sheet satisfying the following (inequality 4), where Q is the luminance in the direction of regular transmission, when visible light rays are irradiated perpendicular to the antiglare sheet from the transparent base material side, and Q₂₀ is the luminance in the direction 20 degrees from regular transmission, when visible light rays are irradiated perpendicular to the antiglare sheet from the transparent base material side. Log₁₀(Q ₂₀ /Q)<−5.5  (Inequality 4)

(6) The aforementioned antiglare sheet satisfying the following (inequality 5), where Ha (%) is the total haze value of the antiglare sheet and Hi (%) is the internal haze value of the antiglare sheet. 0≦Ha−Hi≦1.3  (Inequality 5)

(7) The aforementioned antiglare sheet having an anti-reflection antiglare layer formed on the uppermost surface layer.

(8) A polarizing plate employing the aforementioned antiglare sheet.

(9) An image display device employing the aforementioned antiglare sheet or the aforementioned polarizing plate.

(10) A method for producing an antiglare sheet having an antiglare layer comprising a binder resin, diffusion particles and binder fine particles on at least one side of a transparent base material, the antiglare layer having irregularities on the side opposite the transparent base material, the irregularities being formed by raised sections constituted by the diffusion particles and/or the diffusion particle aggregates, that are surrounded by a localization layer with high density of the binder fine particles, wherein the antiglare sheet is adjusted so as to satisfy the following (inequality 1) and (inequality 2), Q representing the luminance in the direction of regular transmission, when visible light rays have been irradiated on the antiglare sheet perpendicular to the transparent base material side, Q₃₀ representing the luminance in a direction 30 degrees from regular transmission, and U representing the mean value of the transmission intensity determined by extrapolation of a straight line connecting the luminance in the direction +2 degrees from regular transmission with the luminance in the direction +1 degree from regular transmission, and a straight line connecting the luminance in the direction −2 degrees from regular transmission with the luminance in the direction −1 degree from regular transmission, to regular transmission. 10<Q/U<36  (Inequality 1) Log₁₀(Q ₃₀ /Q)<−6  (Inequality 2)

(11) A method for improving the vivid complexion and blackness, blackness in dark surroundings, antiglare property for dynamic images, glazed black feel and black tightness of an image device, wherein in an image device having on the viewing side of the image display device an antiglare sheet having an antiglare layer comprising a binder resin, diffusion particles and binder fine particles on at least one side of a transparent base material, the antiglare layer having irregularities on the side opposite the transparent base material, the irregularities being formed by raised sections based on the diffusion particles and/or the diffusion particle aggregates, that are surrounded by a localization layer with high density of the binder fine particles, the following (inequality 1) and (inequality 2) are satisfied, Q representing the luminance in the direction of regular transmission, when visible light rays have been irradiated on the antiglare sheet perpendicular to the transparent base material side, Q₃₀ representing the luminance in a direction 30 degrees from regular transmission, and U representing the mean value of the transmission intensity determined by extrapolation of a straight line connecting the luminance in the direction +2 degrees from regular transmission with the luminance in the direction +1 degree from regular transmission, and a straight line connecting the luminance in the direction −2 degrees from regular transmission with the luminance in the direction −1 degree from regular transmission, to regular transmission. 10<Q/U<36  (Inequality 1) Log₁₀(Q ₃₀ /Q)<−6  (Inequality 2)

(12) The aforementioned method for improving the vivid complexion and blackness, blackness in dark surroundings, antiglare property for dynamic images, glazed black feel and black tightness of an image device, wherein the specific gravity of the binder fine particles is greater than the specific gravity of the binder resin.

(13) The aforementioned method for improving the vivid complexion and blackness, blackness in dark surroundings, antiglare property for dynamic images, glazed black feel and black tightness of an image device, wherein the binder fine particles are hydrophobic-treated fumed silica and/or a laminar inorganic compound.

(14) The aforementioned method for improving the vivid complexion and blackness, blackness in dark surroundings, antiglare property for dynamic images, glazed black feel and black tightness of an image device, wherein the following (inequality 3) is satisfied, T (μm) being the thickness of the antiglare layer. 3<T<10  (Inequality 3)

(15) The aforementioned method for improving the vivid complexion and blackness, blackness in dark surroundings, antiglare property for dynamic images, glazed black feel and black tightness of an image device, wherein the following (inequality 4) is satisfied, Q being the luminance in the direction of regular transmission when visible light rays are irradiated perpendicular to the antiglare sheet from the transparent base material side, and Q₂₀ being the luminance in a direction 20 degrees from regular transmission, when visible light rays are irradiated perpendicular to the antiglare sheet from the transparent base material side. Log₁₀(Q ₂₀ /Q)<−5.5  (Inequality 4)

(16) The aforementioned method for improving the vivid complexion and blackness, blackness in dark surroundings, antiglare property for dynamic images, glazed black feel and black tightness of an image device, wherein the following (inequality 5) is satisfied, Ha (%) being the total haze value of the antiglare sheet and Hi (%) being the internal haze value of the antiglare sheet. 0≦Ha−Hi≦1.3  (Inequality 5)

(17) The aforementioned method for improving the vivid complexion and blackness, blackness in dark surroundings, antiglare property for dynamic images, glazed black feel and black tightness of an image device, wherein a low refractive index layer is formed on the uppermost surface layer of the antiglare sheet.

Advantageous Effects of Invention

According to the invention it is possible to provide an antiglare sheet for an image display device having a high level of blackness in dark surroundings (blackness in dark surroundings) and excellent vivid complexion and blackness and glazed black feel, and an antiglare property tolerable for dynamic image purposes (an antiglare property for dynamic images), as well as suitability for practical use.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing reflectance by spherical particles and a resin.

FIG. 2 is a graph showing the angles of reflection and transmission with respect to surface inclination angle.

FIG. 3 is a graph showing diffusion intensity distribution.

FIG. 4 is a conceptual drawing illustrating the principle of the evaluation method of the invention.

FIG. 5 is a conceptual drawing showing the method of measuring diffuse transmission intensity according to the invention.

FIG. 6 is a diagram showing the relationship between transmitted scattering angle and reflection proportion on the irregular surface, according to the invention.

FIG. 7-1 is a diagram illustrating the properties of transmitted light and reflected light based on the positional relationship of diffusion particles and surface irregularities for projected light and external light.

FIG. 7-2 is a diagram illustrating the properties of transmitted light and reflected light based on the positional relationship of diffusion particles and surface irregularities for projected light and external light.

FIG. 8-1 is a diagram illustrating differences in diffusion properties of light based on the difference in refractive indexes of diffusion particles and a binder resin.

FIG. 8-2 is a diagram illustrating differences in diffusion properties of light based on the difference in refractive indexes of diffusion particles and a binder resin.

FIG. 8-3 is a diagram illustrating differences in diffusion properties of light based on the difference in refractive indexes of diffusion particles and a binder resin.

FIG. 8-4 is a diagram illustrating differences in diffusion properties of light based on the difference in refractive indexes of diffusion particles and a binder resin.

FIG. 9 is a cross-sectional view showing an embodiment of an antiglare sheet of the invention. This anti-glare sheet 1 has an anti-glare layer 2 provided on a transparent base material 5, and the anti-glare layer 2 comprises a binder resin 4, diffusion particles 3-1 and binder fine particles 3-2.

FIG. 10 is a cross-sectional view showing an embodiment of a polarizing plate using an antiglare sheet of the invention. This polarizing plate 6 has an anti-glare sheet 7 of the invention, a polarized light layer 10, and a transparent base material 11 in this order, and the anti-glare sheet 7 has an anti-glare layer 8 provided on a transparent base material 9.

FIG. 11 is a cross-sectional STEM photograph of an antiglare sheet according to the invention. (a) 3000×, (b) 20,000×

FIG. 12 is a cross-sectional view showing an embodiment of a liquid crystal display device using a polarizing plate of the invention. This liquid crystal display device has a first polarizing plate 12, a first glass panel 13, a color filter 14, a first transparent electrode 15, a liquid crystal cell 16, a second transparent electrode 15, a second glass panel 13, a second polarizing plate 12, and a backlight 17, in this order. The first and second polarizing plates 12 use an anti-glare sheet of the invention.

DESCRIPTION OF EMBODIMENTS

The antiglare sheet of the invention is an antiglare sheet having an antiglare layer comprising a binder resin, diffusion particles and binder fine particles on at least one side of a transparent base material, the antiglare layer having irregularities on the side opposite the transparent base material, the irregularities being formed by raised sections, constituted by the diffusion particles and/or the diffusion particle aggregates, that are surrounded by a localization layer with high density of the binder fine particles, wherein the following inequalities (1) and (2) are satisfied, Q representing the luminance in the direction of regular transmission, when visible light rays have been irradiated on the antiglare sheet perpendicular to the transparent base material side, Q₃₀ representing the luminance in a direction 30 degrees from regular transmission, and U representing the mean value of the transmission intensity determined by extrapolation of a straight line connecting the luminance in the direction +2 degrees from regular transmission with the luminance in the direction +1 degree from regular transmission, and a straight line connecting the luminance in the direction −2 degrees from regular transmission with the luminance in the direction −1 degree from regular transmission, to regular transmission. 10<Q/U<36  (Inequality 1) Log₁₀(Q ₃₀ /Q)<−6  (Inequality 2)

The method of measuring Q and Q₃₀ will now be explained with reference to FIG. 5. When visible light rays are irradiated from direction 5 onto the antiglare sheet for a liquid crystal display device shown in FIG. 5, regular transmission occurs in direction 6, while part of the light is diffused. The transmission intensity in direction 6, i.e. at 0 degrees, is the regular transmission intensity Q. Also, the transmission intensity in the direction of 30 degrees is regular transmission intensity Q₃₀.

The transmission intensities at regular transmission ±2 degrees and regular transmission ±1 degree are measured, the intensities are connected with a straight line, and the average of the transmission intensity extrapolated at regular transmission (0 degrees) is defined as the virtual regular transmission intensity U (see FIG. 4).

In addition, by controlling the material selection and production conditions in the antiglare sheet production process, using Q/U as the index, it is possible to accomplish efficient production of an antiglare sheet with excellent vivid complexion and blackness (for dynamic images) and antiglare properties suitable for dynamic images (antiglare properties for dynamic images), as well as excellent image crispness (for still images).

Specifically, the diffuse transmission intensity is measured in the following manner.

(Method of Measuring Diffuse Transmission Intensity)

Visible light rays are irradiated perpendicular to the back side of the antiglare sheet (the side of the antiglare sheet opposite the observer side). A light beam is directed onto the antiglare sheet and the diffuse transmission intensity of the diffuse transmitted light is measured by scanning with a photodetector one degree at a time in a range of −85 to +85 degrees.

The apparatus used to measure the diffuse transmission intensity is not particularly restricted, but a “GC5000L” by Nippon Denshoku Industries Co., Ltd. was used for the invention. The measurement was carried out in the range of −85 to +85 degrees, but since calculation of the virtual regular transmission intensity and measurement of the regular transmission intensity can be conveniently accomplished by measurement only at −1, −2, 0, +1 and +2 degrees, automatic adjustment within the indicated range can be easily made while varying the production conditions online.

Here, the diameter of the “GC5000L” light beam was approximately 3 mm, the diameter being the average light beam diameter of a commonly used goniophotometer.

Also, since the particle sizes of the diffusion particles used for the invention are on the micron order while the light beam diameter is approximately 1000 times larger than the diameters of the particles that are the internal diffusion factors, or in other words, since with ordinary goniophotometer measurement the light beam diameter is sufficiently larger than the particle sizes and the particles are also uniformly dispersed, no significant difference in measured value is found when the light beam is irradiated at points on a sample, and precise measurement can be accomplished.

The values of Q₃₀, and Q₂₀ which is the transmission intensity in the direction 20 degrees from regular transmission, Q₂₀ being the average value for 20 degrees and −20 degrees and Q₃₀ being the average value for 30 degrees and −30 degrees, are measured by the measuring method described above.

Control using the following inequality (x) as the index is a feature of the invention. Log₁₀(Q ₃₀ /Q)<−6  (x)

By limiting Log₁₀(Q₃₀/Q) to less than −6, it is possible to obtain an antiglare sheet for a liquid crystal display device having excellent vivid complexion and blackness (for dynamic images) and blackness in dark surroundings.

Also, by satisfying the following inequality (y), it is possible to obtain an antiglare sheet for a liquid crystal display device having an even more excellent high level of blackness in dark surroundings. Log₁₀(Q ₂₀ /Q)<−5.5  (y)

When Q₃₀ or Q₂₀ is extremely small so as to be undetectable by the measuring instrument, the value of Log₁₀(Q₃₀/Q) or Log₁₀(Q₂₀/Q) is assumed to be −10.0.

It is another feature of the invention that control is effected using the following inequality (z) as the index. 10<Q/U<36  (z)

If Q/U is greater than 10 the vivid complexion and blackness (for dynamic images) will be excellent, and if it is less than 36, it will be possible to obtain an antiglare sheet for a liquid crystal display device with an excellent antiglare property for dynamic images.

In addition, Q/U is even more preferably greater than 22 and less than 36, since the vivid complexion and blackness and the antiglare property for dynamic images will be further improved.

The antiglare sheet for a liquid crystal display device of the invention satisfies inequalities formula (x) and (z) above. An antiglare sheet for a liquid crystal display device satisfying inequalities (x) and (z) above has an excellent high level of blackness in dark surroundings (blackness in dark surroundings) and excellent vivid complexion and blackness and glazed black feel, and therefore serves as an antiglare sheet for a liquid crystal display device having an antiglare property that is tolerable for dynamic images (antiglare property for dynamic images).

In the antiglare sheet of the invention, the antiglare layer comprises the diffusion particles, the binder resin and the binder fine particles locally concentrated around the diffusion particles.

The binder fine particles that are to be localized around the diffusion particles may be in contact with the diffusion particles, but they do not need to be in complete contact, and they are preferably infiltrating between the binder resin. This can effectively control cure shrinkage of the binder around the diffusion particles. That is, being locally concentrated around the diffusion particles is a state with few of the binder fine particles being present separately in the antiglare layer and most of them being concentrated around the diffusion particles, and such a state can be easily discriminated by cross-section electron microscope (TEM, STEM) observation of the antiglare layer.

Also, the diffusion particles preferably form aggregates. For aggregates, the outer edge sections of the aggregates have irregularities similar to the dispersed particles, whereas the particles composing the aggregates are in close contact with each other, so that the aggregate surfaces form gentle irregularities. In other words, forming aggregates can decrease the large slope components and further increase the soft components. Here, “aggregation” means not only a state where the particles are in complete close contact with each other, but also aggregation in which the distances between the most adjacent particles are smaller than the mean particle sizes of the particles, in observation of a cross-section. The mean particle size (μm) is determined by transmission observation of the particles with a transmission optical microscope, and calculating the average of the maximum diameters of 10 particles. Image analysis software may be used for the calculation.

FIGS. 11(a) and (b) show an example of an antiglare layer in which the binder particles are localized around the diffusion particles as explained above, and the diffusion particles form aggregates. The STEM cross-sectional photographs are at magnifications of 3000× in (a) and 20,000× in (b). This state is preferred because the surface irregularities have no large slope components.

Also, the diffusion particles are preferably present on the transparent base material sides of the sides of the lowest recesses on the outer surface of the irregularities of the antiglare layer, when observed in a cross-section of the antiglare layer. This will avoid protrusion of the diffusion particles, allowing the slopes of the raised sections to be more effectively softened.

In addition to specifying Q/U, Log₁₀ (Q₃₀/Q) and Log₁₀(Q₂₀/Q), the performance of the antiglare sheet for a liquid crystal display device used on the surface of a liquid crystal display unit can be further improved by careful selection of the relationship between the thickness of the antiglare layer, i.e. the thickness T (μm) of the antiglare layer containing the binder resin, the diffusion particles and the binder fine particles, the total haze Ha (%) of the antiglare sheet for a liquid crystal display device, the haze Hi (%) produced by internal diffusion, and the diffusion as the sum of interaction between diffusion due to the irregularities on the surface (hereunder also referred to as “external diffusion”) and diffusion due to internal diffusion, (Ha−Hi), as well as the combination of binder resins in the antiglare layer, and the transparent base material resin.

Cracks will sometimes occur under the load applied to the antiglare sheet by bending during the polarizing plate formation steps or attachment between the polarizing plate and liquid crystal device, and peeling will tend to occur at the interface particularly when bonding between the binder and fine particles is weak. If the thickness of the diffusion layer is large, strain at the interface will be increased by polymerization shrinkage, and peeling will tend to occur more easily, and therefore the thickness T (μm) of the antiglare layer preferably satisfies: 3<T<10.  (Inequality 3)

That is, if the thickness T of the antiglare layer is 3 μm or smaller the hard coat property will be inferior, and if it is 10 μm or greater, strain at the interface with the particles will be increased, tending to result in cracking under load applied to the antiglare sheet.

A small internal diffusion will not allow glare to be eliminated. However, since the presence of internal diffusion with a diffusion angle of 2.5 degrees or greater counts as haze Hi produced by internal diffusion, it is sufficient to have a suitable amount of internal diffusion, even if Hi is zero. However, excessively large diffusion at a large diffusion angle, i.e. internal haze Hi counted as haze, lowers the resolution and significantly reduces contrast due to lower blackness in dark surroundings as a result of generated stray light components, while also further impairing the image crispness (for still images).

Although contrast is reduced, an internal haze of 3.0 or greater can improve the black tightness due to a viewing angle widening effect.

The fundamental concept of the present invention is based on knowledge that the total haze is not the sum of internal diffusion and surface diffusion as understood according to the prior art, but rather that the total haze is affected by the positional relationship of the diffusion factors, in addition to internal diffusion and surface diffusion, or in other words, the total haze is internal haze+external haze+haze due to the interaction between internal diffusion factors and surface irregularities.

Consequently, if the haze of the antiglare sheet for a liquid crystal display device is represented as Ha and the haze produced by internal diffusion is represented by Hi, then Ha−Hi may be considered to be the sum of external haze and haze due to interaction between the internal diffusion factors and surface irregularities.

When viewing dynamic images, a lower haze (Ha−Hi) is preferred since vivid complexion and blackness is desirable to realize high image quality for the dynamic images, and the antiglare property for dynamic images is sufficient if the outlines of virtual images are only slightly visible (weaker than the antiglare property for still images). Also, since haze is not counted as haze when the diffusion angle is less than 2.5 degrees, even if the haze (Ha−Hi) is zero which has conventionally been considered unsuitable, the Q/U value need only be within the desired range, and it is more preferably between 0% and 1.3%.

From the viewpoint of preventing glare, the ratio D of the value with a 2.0 mm optical comb with respect to a 0.125 mm optical comb, as the transmission image clarity of the antiglare sheet based on JIS K7105, is preferably less than 2.

The value with a 0.125 mm optical comb represents the size of diffusion near regular transmission (a smaller value indicating greater diffusion), which is a cause of minute distortion of the projected light, or glare. The value with a 2.0 mm optical comb, on the other hand, represents the size of diffusion in a wider range, i.e. the effect of rendering glare unnoticeable, with a larger value indicating a smaller effect. Thus, the transmission image clarity represents poorer glare as the value is smaller with a 0.125 mm optical comb and as the value is higher with a 2.0 mm optical comb.

This relationship can therefore be represented by D mentioned above, and glare begins to become noticeable when the value is 2 or greater. The value of D is more preferably less than 1.9, and even more preferably less than 1.4.

The diffusion particles dispersed in the binder resin will now be described in detail. The diffusion particles are preferably translucent fine particles, and they may be organic particles or inorganic particles, or a mixture of organic particles and inorganic particles may be used. Spherical organic particles facilitate control of the irregular shapes, and therefore the particles preferably include at least one type of spherical organic particles.

The mean particle size of the diffusion particles used in the antiglare sheet for a liquid crystal display device of the invention is in the range of 0.5 to 10 μm, more preferably 1 to 9 μm and most preferably 1.5 to 8.0 μm. Within this range it is possible to adjust the diffuse transmission intensity distribution by internal diffusion and/or external diffusion and/or by interaction between the internal diffusion factors and surface irregularities.

If the mean particle size of the diffusion particles is at least 0.5 μm, the aggregation of particles will not be excessive and it will be easy to adjust formation of the irregularities, while if it is no greater than 10 μm, images with glare and shine will be prevented and a greater degree of design freedom will be ensured for the diffuse transmission intensity distribution.

In order to satisfy the aforementioned properties specified by the present application, the relationship between the mean particle size R of the diffusion particles and the antiglare layer thickness T preferably satisfies the following inequality. 0.35<R/T<0.65

If the ratio R/T of the mean particle size with respect to the antiglare layer thickness is 0.65 or greater the diffusion particles may protrude through the outer surface of the coating film layer and the irregularities produced by the diffusion particles may become steep. If R/T is 0.35 or smaller, the irregularities may not sufficiently form and virtual images may become more prominent. By satisfying the above inequality it will be possible to form suitable irregular shapes.

For measurement of separate diffusion particles, the mean particle size can be measured as the weight average diameter (volume average diameter), by the Coulter counter method. The mean particle size of the diffusion particles in the antiglare layer, on the other hand, is determined as the average value of the maximum diameters of 10 particles, upon observing the antiglare layer with a transmission optical microscope. If such measurement is unsuitable, it is instead the value obtained from observation with an electron microscope (preferably a transmission type such as TEM or STEM) of a cross-section passing near the center of the particle, selecting 30 diffusion particles observed to be of the same type and to have approximately the same particle sizes (increasing by number n since the locations of the cross-sections in the particles are unknown), measuring the maximum particle sizes of the cross-sections and calculating the average value. Judgment is made from images, and therefore calculation may be made with image analysis software.

Lower variation in the particle size of the diffusion particles will also result in lower variation in the diffusion property, thus facilitating design of the diffuse transmission intensity distribution. More specifically, (d75−d25)/MV is preferably no greater than 0.25 and more preferably no greater than 0.20, where MV is the mean diameter based on the weight average, d25 is the cumulative 25% diameter and d75 is the cumulative 75% diameter.

The cumulative 25% diameter is the particle size constituting 25 wt %, counting from the particles with small particle size among the particle size distribution, and the cumulative 75% diameter is the particle size constituting 75 wt %, counting in the same manner.

As an example of adjusting the variation in particle size, the synthesis reaction conditions may be modified, while classification after synthesis reaction is also an effective means. With classification, the frequency may be increased or the degree intensified to obtain particles with the preferred distribution. The method used for classification is preferably an air classification method, centrifugal classification method, precipitating classification method, filtering classification method, electrostatic classification method or the like.

The difference in refractive index between the binder resin composing the antiglare layer and the diffusion particles is preferably 0.005 to 0.25. If the difference in refractive index is 0.005 or greater it will be possible to prevent glare, and if it is no greater than 0.25 the diffuse transmission intensity distribution design will be facilitated. From this viewpoint, the difference in refractive index is more preferably 0.01 to 0.2 and even more preferably 0.015 to 0.15.

The refractive index of the diffusion particles is measured by measuring the turbidity with dispersion of equal amounts of the diffusion particles in solvents with varying refractive indexes, obtained by varying the mixing ratio with two different solvents having different refractive indexes, measuring the refractive index of the solvent at minimum turbidity using an Abbe refractometer, or by using a Cargille reagent.

The refractive indexes of the diffusion particles can be determined by measuring the material itself, or otherwise it can be measured by a method in which the particles or fragments of the particles are removed from the film after the antiglare sheet for a liquid crystal display device has been actually formed and measurement is performed by the method described above, or by a method in which a cut surface of the antiglare sheet is measured with an ellipsometer, or by a method in which the laser interference of the antiglare sheet is measured (using a phase-shift laser interference microscope by FK Opt Labo Co., Ltd., or a light beam interference microscope by Mizojiri Optical Co., Ltd.).

When the diffusion particles are organic particles having a different refractive index than the binder, with an impregnation layer in which components in the coating solution have penetrated the organic particles, and the components in the coating solution have not impregnated to the center sections of the organic particles, this is more preferred because the difference in refractive index at the interface between the organic particles and the binder resin will be small and reflection at the interface will be limited, thereby minimizing generation of stray light, while the organic particle interiors will have a large difference in refractive index with the binder resin so that internal diffusion will be maintained, and therefore both stray light generation and glare can be prevented.

In order to increase the amount of impregnation of the impregnation layer, for example, the crosslink density of the organic particles may be lowered, an impregnating solvent may be used therewith, or the coating solution storage temperature may be increased, and the conditions for the preferred amount of impregnation must be set beforehand.

From the viewpoint of maintaining internal diffusion performance for organic particles having such an impregnation layer, the center sections not impregnated with the components of the coating solution preferably have diameters of at least the wavelength of visible light, and more preferably they have diameters of at least 1 μm.

For the diameters of the non-impregnated portions of the center sections, specifically, the mean diameter of the particles in the antiglare layer may first be calculated by observation with a transmission optical microscope as described above, and a cross-section of the antiglare layer may be observed with a STEM at 3000× to 50,000×, at five arbitrary locations that definitely include at least one fine particle of the impregnation layer, and after photographing, the section with maximum impregnation may be measured and the average value (average value of 5 or more particles) calculated. It may be calculated by subtracting the average value of the impregnated portion from the value of the original mean particle size.

As translucent organic particles there may be used polymethyl methacrylate particles, polyacryl-styrene copolymer particles, melamine resin particles, polycarbonate particles, polystyrene particles, polyvinyl chloride particles, benzoguanamine-melamine-formaldehyde particles, silicone particles, fluorine-based resin particles, a polyester-based resin, or the like, or organic particles with hollows or pores.

When organic particles are used, and the binder particles are inorganic fine particles (having hydrophilic surfaces when untreated), the surfaces of the organic particles may be hydrophilicized in order to allow the binder fine particles to be satisfactorily localized around the organic particles. The hydrophilicizing treatment may be by a known method without any particular restrictions, and for example, it may be a method of copolymerizing a monomer with functional groups such as carboxylic acid groups or hydroxyl groups on the surfaces of the organic particles.

Translucent inorganic particles include silica particles, alumina particles, zirconia particles, titania particles, talc, mica, kaolin, smectite, bentonite particles, or hollow or porous inorganic particles.

The diffusion particles preferably have spherical shapes as single particles. If the single diffusion particles are spherical, the light diffusion angle of the particles will not be very large and it will be possible to minimize generation of stray light components, so that an antiglare property sheet with excellent vivid complexion and blackness can be obtained.

The term “spherical” includes exactly spherical and elliptical spherical, but excludes amorphous shapes with angular sections or with many light-diffusing sections.

The diffusion particles are also preferably organic particles. If they are organic particles, an impregnation layer will more easily form, and because the specific gravity is low, they will move more easily in the coating film after application to facilitate formation of aggregates of the diffusion particles, while it will also be possible to inhibit precipitation of the diffusion particles in the coating solution.

There are no particular restrictions on the content of the diffusion particles in the coating solution, but it is preferably 0.5 to 30 parts by weight with respect to 100 parts by weight of the radiation curable translucent resin described below. If it is less than 0.5 part by weight it will not be possible to form sufficient irregular shapes on the surface of the antiglare layer, and the antiglare sheet of the invention will have an inadequate antiglare property for dynamic images.

If it is greater than 30 parts by weight, on the other hand, aggregation will occur between the diffusion particles in the coating solution, large raised sections may be formed on the surface of the antiglare layer making it impossible to obtain the desired performance, and discoloration or glare may be produced.

A more preferred lower limit for the content of the diffusion particles is 1 part by weight, and a more preferred upper limit is 20 parts by weight. This range will allow the aforementioned effect to be more reliably exhibited.

The binder fine particles preferably have particle sizes of 1 nm or greater and smaller than the diffusion particles, readily aggregate in the binder resin, and have a larger specific gravity than the binder resin, and the aforementioned translucent inorganic particles may be used. In particular, there may be used a laminar inorganic compound such as talc or smectite, or fumed silica, preferably having a hydrophobicized surface.

The specific gravity may be measured by a liquid phase exchange method or gas phase exchange method (pycnometer method).

The binder fine particles are more preferably fumed silica, for high stability in the coating solution.

The term “fumed silica” refers to amorphous silica having particle sizes of no greater than 200 nm, formed by a dry method, and it can be obtained by reacting a silicon-containing volatile compound in a gas phase. Specifically, it may be a substance produced by hydrolysis of a silicon compound such as SiCI₄ in an oxygen and hydrogen flame. Examples of fumed silica products include AEROSIL by Nippon Aerosil Co., Ltd.

Fumed silica preferably has a mean primary particle size of 1 to 100 nm. If it is less than 1 nm, it may not be possible to sufficiently form the aforementioned aggregates, and if it exceeds 100 nm, stray light components may be generated by the aggregates. A more preferred lower limit is 5 nm, and a more preferred upper limit is 50 nm. The mean primary particle size is the value measured from a transmission electron microscope (TEM or STEM) image, using image processing software.

When the antiglare layer is observed by microscopy with STEM or the like, fumed silica with a mean primary particle size in the aforementioned range is found to aggregate and be linked into a bead-like macrostructure. Whether such a macrostructure is formed, the mean particle size of the maximal portion of the aggregates is preferably 20 to 600 nm as this will allow high transmittance to be maintained for the antiglare layer. If it exceeds 600 nm, this may result in reduced transparency and generation of stray light components. It is more preferably 20 to 400 nm.

The mean particle size of the macronized fumed silica is calculated as the average value of the maximum diameters of 10 macroparticles, as observed in a cross-section of the antiglare layer by STEM.

Also, the surfaces of the fumed silica are preferably surface-treated, and preferably hydrophobicized. By such surface treatment it is possible to distribute the fumed silica preferentially on the surfaces of the organic fine particles, and to form diffusion particle aggregates of organic fine particles or the like when the fumed silica aggregates together. In addition, it is possible to impart chemical resistance and saponification resistance to the fumed silica itself. The hydrophobicizing treatment may be methyl treatment, octylsilane treatment, dimethylsilicone oil method or the like, among which octylsilane treatment is preferred from the viewpoint of hydrophobicity suitable for localization with organic particles.

FIGS. 11(a) and (b) show an example of the antiglare layer 8 according to the invention of FIG. 10, as STEM cross-section photographs at 3000× magnification in (a) and 20,000× magnification in (b). The fumed silica linked in a bead-like fashion is distributed around diffusion particles such as organic particles in a cross-section of the antiglare layer, and several diffusion particles are also aggregated. The aggregated sections form soft raised sections, and are the preferred form for the invention.

The binder resin composing the antiglare layer may be a translucent ionizing radiation curable resin or thermosetting resin. For formation of antiglare layer, a resin composition comprising the ionizing radiation curable resin or thermosetting resin may be coated onto a transparent base material, and the monomer, oligomer and prepolymer in the resin composition may be crosslinked and/or polymerized.

The reactive functional groups of the monomer, oligomer and prepolymer are preferably ionizing radiation-polymerizable, and are especially photopolymerizable functional groups.

As photopolymerizable functional groups there may be mentioned unsaturated polymerizable functional groups such as (meth)acryloyl, vinyl, styryl and allyl.

As prepolymers and oligomers there may be mentioned acrylates such as urethane (meth)acrylate, polyester (meth)acrylate and epoxy (meth)acrylate, and unsaturated polyesters, epoxy resins and the like.

Monomers include styrene-based monomers such as styrene and α-methylstyrene; acrylic monomers such as methyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, pentaerythritol (meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritolethoxy tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropaneethoxy tri(meth)acrylate, glycerin propoxy triacrylate, ditrimethylolpropane tetraacrylate, polyethylene glycol di(meth)acrylate, bisphenol F EO-modified di(meth)acrylate, bisphenol A EO-modified di(meth)acrylate, isocyanuric acid EO-modified di(meth)acrylate, isocyanuric acid EO-modified tri(meth)acrylate, polypropylene glycol di(meth)acrylate, trimethylolpropane PO-modified tri(meth)acrylate, trimethylolpropane EO-modified tri(meth)acrylate and ditrimethylolpropane tetra(meth)acrylate; polyol compounds having 2 or more thiol groups in the molecule, such as trimethylolpropane trithioglycolate, trimethylolpropane trithiopropylate and pentaerythritol tetrathioglycol, and urethane (meth)acrylates or polyester (meth)acrylates having 2 or more unsaturated bonds.

Polyfunctional acrylates are particularly preferred, among which pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate and dipentaerythritol penta(meth)acrylate are more preferred.

As binder resins there may be used polymers added to the resin composition. Polymethyl methacrylate (PMMA) and cellulose acetate propionate (CAP) are examples of such polymers.

Addition of a polymer allows the viscosity of the coating solution to be adjusted, and this is advantageous in that it can facilitate coating while also facilitating modification of irregular shapes formed by particle aggregation and allowing sinking of the particles to be controlled, while it can also control interaction between surface diffusion and internal diffusion and surface irregularities.

The preferred weight-average molecular weight of the polymer is 20,000 to 100,000. If it is less than 20,000, it will be necessary to increase the amount of addition in order to adjust the viscosity, potentially lowering the hardness of the antiglare layer, and if it is 100,000 or greater the viscosity will be too high, potentially lowering the curing property, while the presence of a compound with an excessively high weight-average molecular weight in the composition can inhibit crosslinking during the curing reaction and potentially lower the hardness.

The weight-average molecular weight according to the invention is determined in terms of polystyrene, based on measurement by gel permeation chromatography (GPC) with a THF solvent.

A photoradical polymerization initiator may also be added to the resin composition if necessary. As photoradical polymerization initiators there may be used acetophenones, benzoins, benzophenones, phosphine oxides, ketals, anthraquinones, thioxanthones, azo compounds and the like.

As acetophenones there may be mentioned 2,2-dimethoxyacetophenone, 2,2-diethoxyacetophenone, p-dimethylacetophenone, 1-hydroxy-dimethylphenyl ketone, 1-hydroxy-dimethyl-p-isopropylphenyl ketone, 1-hydroxycyclohexylphenyl ketone, 2-methyl-4-methylthio-2-morpholinopropiophenone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone, 4-phenoxydichloroacetophenone and 4-t-butyl-dichloroacetophenone, and as benzoins there may be mentioned benzoin, benzoinmethyl ether, benzoinethyl ether, benzoinisopropyl ether, benzyldimethylketal, benzoinbenzenesulfonic acid ester, benzointoluenesulfonic acid ester, benzoinmethyl ether, benzoinethyl ether and the like.

As benzophenones there may be used benzophenone, hydroxybenzophenone, 4-benzoyl-4′-methyldiphenyl sulfide, 2,4-dichlorobenzophenone, 4,4-dichlorobenzophenone and p-chlorobenzophenone, 4,4′-dimethylaminobenzophenone (Michler's ketone), 3,3′,4,4′-tetra(t-butylperoxycarbonyl)benzophenone, and the like.

A photosensitizer may also be used therewith in combination, specific examples of which include n-butylamine, triethylamine and poly-n-butylphosphine.

Furthermore, addition of fine particles that are no larger than 100 nm, and have a high refractive index or low refractive index, to the ionizing radiation curable resin or thermosetting resin will modify the refractive index of the transparent resin to allow control of internal diffusion.

However, when an organosilane is included in the binder resin, cohesion of the particles will vary considerably depending on the combination of the resin in the coating solution, the solvent system and the lipophilicity/hydrophilicity of the particles, resulting in unstable optical characteristics, and therefore it is preferred to avoid using an organosilane.

The reason for this is conjectured to be that, even with one type of particle, differences in volatility of solvents (two or more usually being present) produces changes in the composition during drying, making it difficult to control aggregation and dispersion. This is particularly notable when using two or more different types of particles with different degrees of lipophilicity or hydrophilicity. It can therefore become impossible to control roughness and glare at points where steep irregularities form.

A solvent will usually be added to the radiation-curing resin composition to adjust the viscosity or to allow dissolution or dispersion of each of the components. The type of solvent used will alter the surface condition of the coating film in the coating and drying steps, and it is therefore selected as appropriate in consideration of allowing adjustment of the transmission intensity distribution by external diffusion, and also in consideration of differences in the impregnation layer thickness of the organic fine particles.

Specifically, it is selected in consideration of the saturation vapor pressure and permeability into the transparent base material.

Adjusting the amount of impregnation of the low-molecular-weight components in the coating solution into the transparent base material allows control of the thickness of the antiglare layer, while impregnation into the transparent base material causes the base material surface to become soft and to have a function of absorbing cure shrinkage of the antiglare layer, such that it becomes possible to achieve modification of the shapes of the surface irregularities, as mentioned above. This method is particularly effective when the transparent base material is a cellulose-based resin.

Furthermore, by using a solvent that is capable of being impregnated into particles, it will be easier for at least some of the transparent resin component to permeate into the particles, and the impregnation layer can be adjusted, thereby allowing control of the diffusion transmission intensity.

The solvent may be appropriately selected in consideration of the aforementioned explanation, and specifically there may be mentioned aromatic solvents such as toluene and xylene, and ketones such as methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK) and cyclohexanone, which may be used alone or in combinations of two or more.

It is preferred to use a mixture of at least one type of aromatic solvent and at least one type of ketone. To control the drying speed, there may be combined therewith a cellosolve such as methylcellosolve or ethylcellosolve, a cellosolve acetate, or an alcohol such as ethanol, isopropanol, butanol or cyclohexanol.

Particularly when hydrophobicized fumed silica is used as the binder fine particles, it is preferred to also use a solvent with high polarity and a rapid volatilization rate. With such a solvent, the dispersibility of the fumed silica in the coating solution will be satisfactory, and it will rapidly dry after coating and easily collect in the coating film, to facilitate localization around the diffusion particles. Examples of such solvents include ethanol and isopropanol, with isopropanol being preferred for use.

Additives other than diffusion particles and binder fine particles may also be added to the binder resin in the antiglare sheet of the invention, as necessary.

For example, various surfactants may be used for an anti-aggregation effect and anti-settling effect, as well as to improve the properties such as the leveling property.

As surfactants there are preferred silicone oils and fluorine-based surfactants, and preferably fluorine-based surfactants containing perfluoroalkyl groups, in order to prevent the antiglare layer from exhibiting a Benard cell structure. When the resin composition containing the solvent is coated and dried, a difference in surface tension is produced between the membrane surface and the inner surface in the coated film, whereby multiple convection currents are created within the film. The structure produced by such convection currents is known as a “Benard cell structure”, and it results in an orange peel surface or coating defects.

A Benard cell structure also adversely affects the vivid complexion and blackness (for dynamic images) and image smoothness (otherwise, crispness, or sharp taste) (for still images). When such a surfactant is used it is possible to prevent such convection currents, thus resulting not only in a concavoconvex film without defects or irregularities, but also facilitating adjustment of the transmission scattering and luminance properties.

According to the invention there may also be added stain-proofing agents, antistatic agents, coloring agents (pigments and dyes), flame retardants, ultraviolet absorbers, infrared absorbers, tackifiers, polymerization inhibitors, antioxidants, surface modifiers and the like.

The transparent base material used in the antiglare sheet of the invention is not particularly restricted so long as it is commonly used in antiglare sheets for image display devices, and it may be a transparent resin film, transparent resin plate, transparent resin sheet, transparent glass or the like.

As transparent resin films there may be used triacetyl cellulose films (TAC films), diacetyl cellulose films, acetylbutyl cellulose films, acetylpropyl cellulose films, cyclic polyolefin films, polyethylene terephthalate films, polyethersulfone films, polyacrylic-based resin films, polyurethane-based resin films, polyester films, polycarbonate films, polysulfone films, polyether films, polymethylpentene films, polyetherketone films, (meth)acrylonitrile films, polynorbornane-based resin films and the like.

In particular, in addition to facilitating smoothness of the surface irregularities in order to have an impregnating property, a TAC film is preferred when the antiglare sheet for an image display device of the invention is to be used together with a polarizing plate, since it does not interfere with polarized light, a cyclic polyolefin film is preferred for weather resistance, and a polyester film such as a polyethylene terephthalate film is preferred if emphasis is on mechanical strength and smoothness.

The transparent base material may be a multilayer or monolayer material, and a primer layer may also be provided on the surface for adhesion with the coating film.

Also, in order to prevent interference patterns produced at the interface when a substantial difference in refractive index exists between the transparent base material and coating film layer, for example, an anti-interference pattern layer with a refractive index intermediate between that of the transparent base material and the coating film layer may be provided between them, or irregularities of about 0.3 to 1.5 μm may be formed as surface roughness (ten-point height of irregularities: Rz), in addition to using a coating solution that impregnates the transparent base material.

Rz is the value measured with a cutoff value of 2.5 mm and an evaluating speed of 0.5 mm/s, based on the method of JIS B0601 1994.

Functions such as a hard coat property, prevention of unwanted reflection, anti-reflection, an antistatic property or an antifouling property may be imparted to the antiglare sheet of the invention. The hard coat property is usually evaluated based on the pencil hardness (measured according to JIS K5400), or by a 10-pass abrasion test using steel wool #0000 under a load, evaluating the maximum load under which no damage is observed with black tape attached to the back side (steel wool scuff resistance).

The pencil hardness of the antiglare sheet of the invention is preferably H or greater, and more preferably 2H or greater.

For the steel wool scuff resistance, the maximum load where no damage was observed even with a 10-pass abrasion test is preferably 200 g/cm² or greater, more preferably 500 g/cm² or greater and most preferably 700 g/cm² or greater.

Antistatic performance is preferably imparted from the viewpoint of preventing static electricity on the antiglare sheet surface.

To impart antistatic performance, there may be mentioned methods known in the prior art, such as a method of coating a conductive coating solution comprising conductive fine particles, a quaternary ammonium salt, polythiophene, other conductive organic compounds and the like, and a reactive curing resin, or a method of forming a conductive thin-film by vapor deposition or sputtering of a metal or metal oxide that forms a transparent film.

The antistatic layer may also be used as a portion of a functional layer, such as for hard coating, prevention of unwanted reflection, anti-reflection or the like.

The surface resistance value is an index of the antistatic property, and according to the invention the surface resistance value is preferably no greater than 10¹² Ω/sq., more preferably no greater than 10¹¹ Ω/sq. and especially no greater than 10¹⁰ Ω/sq.

The “saturated electrostatic voltage”, or the maximum voltage at which the optical film can accumulate, is preferably no greater than 2 kV at an applied voltage of 10 kV.

An antifouling layer may also be provided on the outer surface of the antiglare sheet of the invention. An antifouling layer lowers the surface energy and inhibits adhesion of hydrophilic or lipophilic contaminants.

The antifouling layer can be imparted by adding a stain-proofing agent, and as stain-proofing agents there may be mentioned fluorine-based compounds, silicon-based compounds and their mixtures, among which fluoroalkyl group-containing compounds are particularly preferred.

A low refractive index layer with a lower refractive index than the surface layer, with a low refractive index layer laminated on the surface, may additionally be provided on the outer surface of the antiglare sheet of the invention.

The low refractive index layer is a layer with a thickness of about 80 to 120 nm, and it further lowers the reflection of external light by interference. The low refractive index layer is not restricted but is preferably formed by coating and curing a coating solution containing an ultraviolet curing resin to which porous or hollow silica has been added. By coating and curing the coating solution, the fine, sharp irregularities present as raised sections of the antiglare layer surface become smoothed, so that even more improved vivid complexion and blackness can be achieved in addition to an anti-reflection effect.

The antiglare sheet of the invention is produced by coating the resin composition that is to form the antiglare layer with an irregular form on the outermost surface, on a transparent base material.

The coating method may be any of various known methods, such as dip coating, air knife coating, curtain coating, roll coating, wire bar coating, gravure coating, die coating, blade coating, microgravure coating, spray coating, spin coating or reverse coating, for example.

According to the invention, the transmission scattering luminance property varies depending on the coating amount, and therefore roll coating, gravure coating, die coating or reverse coating is preferred, as such methods can facilitate stably obtaining a range of 3 to 10 μm for the sum of the thicknesses of the layer having a diffusion factor in the interior, and the transparent resin layer.

After coating by any of the aforementioned methods, the sheet is transported into a heated zone to dry the solvent, or another known method is used to dry the solvent. By selecting the relative evaporation rate of the solvent, the solid concentration, the coating solution temperature, the drying temperature, the drying air speed, the drying time and the dry zone solvent atmosphere concentration, it is possible to adjust the external diffusion due to the profile of the surface irregularity shapes, and the internal diffusion due to the diffusion particles or additives.

A method of adjusting the transmission scattering luminance property by selection of the drying conditions is particularly preferred and convenient. Specifically, the drying temperature is preferably 30° C. to 120° C. and the drying wind speed is 0.2-50 m/s, since the transmission scattering luminance property can be controlled with appropriate adjustment in this range.

More specifically, controlling the type of solvent and the drying temperature allows adjustment of the permeability of the resin and the solvent into the base material. That is, by controlling the drying temperature, given the same solvent conditions, it is possible to adjust the permeability of the resin and solvent into the base material, and as explained above, this is linked with control of the form of surface irregularities.

After drying the solvent by any of the aforementioned methods, ionizing radiation curing may be performed to cure the coating film.

The type of ionizing radiation used for the invention is not particularly restricted, and it may be appropriately selected from among ultraviolet rays, an electron beam, near-ultraviolet rays, visible light, near infrared rays, infrared rays, X-rays and the like depending on the type of curable composition used to form the coating film, but ultraviolet rays are preferred since they are particularly convenient to use and easily provide high energy.

The light source used for photopolymerization of an ultraviolet ray reactive compound may be any light source that generates ultraviolet rays. For example, a low-pressure mercury lamp, medium-pressure mercury lamp, high-pressure mercury lamp, ultra-high-pressure mercury lamp, carbon arc lamp, metal halide lamp, xenon lamp, fusion lamp or the like may be used. There may also be used an ArF excimer laser, KrF excimer laser, excimer lamp or synchrotron radiation. Among these it is preferred to use a low-pressure mercury lamp, medium-pressure mercury lamp, high-pressure mercury lamp, ultra-high-pressure mercury lamp, carbon arc lamp, metal halide lamp, xenon lamp or fusion lamp.

EXAMPLES

The invention will now be explained in greater detail by examples, with the understanding that the invention is in no way limited by the examples.

Example 1

Triacetyl cellulose (80 μm thickness, FujiFilm Corp.) was prepared as a transparent base material.

As the binder resin there was used a mixture of 70 parts by weight of pentaerythritol tetraacrylate (PETTA, product name: M-451, product of Toagosei Co., Ltd.) and 30 parts by weight of isocyanuric acid PO-modified triacrylate (product name: M-313, product of Toagosei Co., Ltd.) (refractive index: 1.51).

There were added thereto 5 parts by weight of styrene acrylic copolymer particles (refractive index: 1.56, mean particle size: 3.5 μm, product of Sekisui Plastics Co., Ltd.) as diffusion particles, and 4 parts by weight of talc (Nanotalc D-1000, mean particle size: 1.0 μm, product of Nippon Talc Co., Ltd.) as binder fine particles, with respect to 100 parts by weight of the binder resin.

There were also added the initiator IRGACURE 184 (product of BASF, Japan) and the leveling agent polyether-modified silicone oil (TSF4460, product of Momentive Performance Materials, Inc.), at 5 parts by weight and 0.04 part by weight, respectively, with respect to 100 parts by weight of the binder resin.

A resin composition obtained by mixing a mixed solvent of toluene, isopropanol and cyclohexanone (weight ratio: 7:2:1) as the solvent at 190 parts by weight with respect to 100 parts by weight of the binder resin, was coated onto the transparent base material, dry air at 70° C. was circulated at a flow rate of 0.2 m/s for 15 seconds, and dry air at 70° C. was further circulated at a flow rate of 10 m/s for 30 seconds, for drying.

Next, it was irradiated with ultraviolet rays (200 mJ/cm² under a nitrogen atmosphere) to cure the binder resin, to fabricate an antiglare sheet. The cured antiglare layer thickness was 5.5 μm.

Examples 2 to 10 Comparative Examples 1 to 5

Antiglare sheets were fabricated in the same manner as Example 1, except that the components added to the coating solution and the conditions were as listed in Tables 1 and 2.

TABLE 1 Diffusion particles Binder fine particles Added Added amount amount (pts. by (parts by Binder Type wt.) Type wt.) resin Solvent Example 1 α 5 a 4 P X Example 2 α 10 a 4 P X Example 3 β 2 a 3 P X Example 4 β 3 b 1 P X Example 5 α 13 a 5 P X Example 6 α 10 b 1 P X Example 7 α 8 b 1 P X Example 8 α 6 a 3 P X Example 9 β 3 b 1 P X Example 10 α 5 a 6 P X Comp. Ex. 1 β 5 b 1 P X Comp. Ex. 2 β 5 a 9 P X Comp. Ex. 3 β 9 None — Q Y Comp. Ex. 4 γ 10 b 2 P X Comp. Ex. 5 γ 12 None — Q Y

TABLE 2 T (μm) Vivid Anti-glare Anti-glare complex-ion property for Blackness in Glazed Log₁₀ Log₁₀ Ha- layer and dynamic dark Black black HC Q/U (Q₃₀/Q) (Q₂₀/Q) Hi Hi thickness blackness images surroundings tightness feel Cracking property Example 1 20.1 −10.0 −5.9 0.3 4.0 5.5 F VG G G G G G Example 2 21.0 −6.3 −5.3 0.5 10.0 5.9 F VG F G G G G Example 3 24.0 −10.0 −10.0 0 0.8 3.8 G VG VG F VG G G Example 4 35.3 −10.0 −10.0 0 2.5 5.5 VG G VG F VG G G Example 5 10.5 −6.1 −4.2 0.9 12.0 6.0 F VG F G G G G Example 6 33.0 −6.1 −4.5 0.4 11.0 7.5 G VG F G G G G Example 7 34.0 −10.0 −4.8 0.6 9.5 8.0 VG G F G G G G Example 8 29.5 −10.0 −5.6 0.2 7.1 8.8 G VG G G G G G Example 9 33.2 −10.0 −10.0 0.2 1.8 4.2 VG VG VG F VG G G Example 15.9 −10.0 −10.0 1.2 5.8 7.8 F VG VG G F G G 10 Comp. 38.8 −10.0 −6.2 0.2 9.3 10.5 VG P VG G G P G Ex. 1 Comp. 8.7 −10.0 −10.0 1.3 3.0 3.7 P P VG F F G G Ex. 2 Comp. 7.0 −10.0 −10.0 1.6 5.0 2.8 P P VG G P G P Ex. 3 Comp. 21.0 −5.5 −4.5 0.8 20.1 5.8 F VG P G G G G Ex. 4 Comp. 7.1 −5 −4.2 2.4 22.6 4.0 P P P G P G G Ex. 5

In Table 1, the details regarding the symbols indicated for the diffusion particles, binder fine particles, binder resin and solvent are as follows.

(Diffusion Particles)

α: Styrene acrylic copolymer particles (refractive index: 1.56, mean particle size: 3.5 μm, product of Sekisui Plastics Co., Ltd.)

β: Styrene acrylic copolymer particles (refractive index: 1.54, mean particle size: 2.0 μm, product of Sekisui Plastics Co., Ltd.)

γ: Polystyrene particles (refractive index: 1.60, mean particle size: 3.0 μm, product of Sekisui Plastics Co., Ltd.)

(Binder Fine Particles)

a: Talc (Nanotalc D-1000, mean particle size: 1.0 μm, product of Nippon Talc Co., Ltd.)

b: Hydrophobicized fumed silica (mean primary particle size: approximately 12 nm, product of Nippon Aerosil Co., Ltd.)

(Binder Resin)

P: Mixture of 70 parts by weight of pentaerythritol tetraacrylate (PETTA, product name: M-451, product of Toagosei Co., Ltd.) and 30 parts by weight of isocyanuric acid PO-modified triacrylate (product name: M-313, product of Toagosei Co., Ltd.) (refractive index: 1.51).

Q: Mixture of 80 parts by weight of pentaerythritol triacrylate (PET-30, product of Nippon Kayaku Co., Ltd.), 5 parts by weight of dipentaerythritol hexaacrylate (DPHA, product of Nippon Kayaku Co., Ltd.) and 15 parts by weight of polymer acrylate (BS 371, product of Arakawa Chemical Industries, Ltd.) (refractive index: 1.51).

(Solvent)

X: Mixture of toluene, isopropanol and cyclohexanone (weight ratio: 7:2:1).

Y: Mixture of toluene and cyclohexanone (weight ratio: 6:4).

[Evaluation Methods]

1. Film Thickness: T (μm) Measurement Method

A confocal microscope (LeicaTCS-NT: product of Leica Microsystems GmbH, objective lens, 10-100× magnification) was used for observation of a cross-section of the antiglare sheet, and the presence or absence of an interface was evaluated on the following scale.

Measurement Procedure

(1) In order to obtain clear images without halation, observation was made using a wet objective lens in a confocal microscope, placing approximately 2 ml of oil with a refractive index of 1.518 on the optical laminate. The oil was used to eliminate the air layer between the objective lens and the antiglare layer.

(2) The film thickness from the base material was measured at a maximum height and minimum recess in the irregularities in a single screen, at 1 point each for a total of 2 points, measuring 5 screens for a total of 10 points, and the mean value was calculated as the antiglare layer thickness. In cases where the interface is not distinct under the confocal microscope, a cross-section of the antiglare sheet can be prepared with a microtome and observed with an electron microscope, and the film thickness can be calculated in the same manner as (2) above.

2. Total Haze: Ha (%) Measurement Method

The total haze value can be measured according to JIS K-7136 (2000). The device used for measurement was an HM-150 haze meter (Murakami Color Research Laboratory Co., Ltd.). The haze is measured with the transparent base material surface facing the light source.

3. Internal Haze: Hi (%) Measurement Method

The internal haze used for the invention was determined in the following manner. The irregularities on the outermost surface on the observer side of the antiglare sheet were coated with a resin having a refractive index equivalent to that of the resin forming the surface irregularities, or at least with a difference in refractive index of no greater than 0.02, and with the fine particles removed from the examples and comparative examples for the present invention, using a wire bar for coating to a dry film thickness of 8 μm (a film thickness where the surface irregular shapes completely disappear and a flat surface can be formed), and after drying at 70° C. for 1 minute, it was irradiated with ultraviolet rays at 100 mj/cm² for curing.

This crushes the irregularities on the surface to form a flat surface. However, when the presence of a leveling agent in the composition used to form the antiglare layer with an irregular shape causes cissing of the recoating agent and inhibits wetting, the antiglare sheet may be pretreated with hydrophilic treatment by saponification (immersion in a 2 mol/l NaOH (or KOH) solution at 55° C. for 3 minutes, followed by rinsing and complete removal of water droplets with a Kimwipe, and then 1 minute of drying in an oven at 50° C.)

The surface-flattened sheet has only internal haze, because it has no surface irregularities and no interaction.

The haze of the sheet can be measured by the same method as for the total haze according to JIS K-7136, and determined as the internal haze.

The haze of the triacetyl cellulose base material itself used in the examples of the invention was 0.2. The internal haze of the antiglare layer itself is the haze of this base material subtracted from the internal haze, but according to the invention it is not subtracted. Since an image display device generally has an antiglare layer as a layered body, it is more practical to consider not only the internal haze of the antiglare layer alone, but also the internal haze of the entire layered body. For example, while the influence is low with a haze of about 0.2, when a base material with high haze is used, subtracting it will result in a different evaluation of the optical characteristics as a layered body.

4. Measurement of Regular Transmission Intensity Q, Virtual Regular Transmission Intensity U, Q₂₀ and Q₃₀.

This was measured for each of the antiglare sheets fabricated in the production examples, by the methods described throughout the present specification.

5. Hard Coat Property Evaluation Method

“Hardness”, for an antiglare sheet of the invention, is pencil hardness of 2H or greater in a pencil hardness test.

The pencil hardness can be measured according to JIS K-5400. The device used for measurement may be a pencil hardness tester (product of Toyo Seiki Co., Ltd.). The pencil hardness test determines the hardness of a pencil used without outer defects such as scratches in at least 4 of 5 pencil hardness tests. For example, when a 2H pencil is used for 5 tests, and no outer defects occur in 4 tests, the pencil hardness of the optical laminate is recorded as 2H.

G: Pencil hardness of 2H or greater.

P: Pencil hardness of less than 2H.

6. Cracking Evaluation Method

The antiglare sheet was wrapped around the core rod of a cylindrical mandrel used in the bending test of JIS K5600-5-1, and evaluation was performed based on generation of cracks.

G: Satisfactory without generation of cracks, even when wound around an 8 mm core rod.

P: Generation of cracks when wound around an 8 mm core rod.

7. Evaluation of Images

The polarizing plate on the outer surface of a “KDL-40X2500” liquid crystal television by Sony Corporation was released and a polarizing plate without a surface coating layer was attached.

Next, a sample produced by each production example and comparative example was attached thereover with the antiglare layer side as the outer surface, using a transparent pressure-sensitive adhesive film for an optical film (product with total light transmittance: ≧91%, haze: ≦0.3%, film thickness: 20 to 50 μm, such as one of the MHM Series by Nichiei Kakoh Co., Ltd.).

The liquid crystal television was set in a room in an environment with an illuminance of about 1,000 Lx, the DVD “Phantom of the Opera” by Media Factory, Inc. was displayed thereon, and the image was viewed by 15 subjects from a location about 1.5-2.0 m distant from the liquid crystal television, at different vertical and horizontal angles, for sensation evaluation of the following properties. The evaluation levels were as follows.

(1) Vivid complexion and blackness: For display of dynamic images, this was judged based on high contrast (glazed black feel and black tightness), with stereoscopic visual effect, gloss and brightness in the image, and sense of motion.

VG: Evaluation of G for both stereoscopic visual effect and sense of motion.

G: Evaluation of G for either stereoscopic visual effect or sense of motion, and evaluation of F for the other.

F: Evaluation of F for both stereoscopic visual effect and sense of motion.

P: Evaluation of P for either stereoscopic visual effect or sense of motion.

The stereoscopic visual effect and sense of motion were evaluated on the following scale.

Stereoscopic Visual Effect

G: Evaluation of “satisfactory” by at least 10 individuals.

F: Evaluation of “satisfactory” by 5-9 individuals.

P: Evaluation of “satisfactory” by 4 or fewer individuals.

Sense of Motion

G: Evaluation of “satisfactory” by at least 10 individuals.

F: Evaluation of “satisfactory” by 5-9 individuals.

P: Evaluation of “satisfactory” by 4 or fewer individuals.

(2) Antiglare property for dynamic images: For display of dynamic images, this was judged based on excellent prevention of unwanted reflection (a condition without disturbance by virtual images of observer or observer background), and visibility of dynamic images. A condition of acceptable virtual images of the observer or observer background is a condition in which the presence of the observer is visible but the outlines are indistinctly halated, and the presence of background objects is also visible but the outlines or borders are indistinct. It is also a condition in which, when the background is a white wall, the presence of the white wall is visible but the whiteness is halated and the borders of the wall are indistinct. Thus, simple halation of the outlines results in virtual images becoming no inconvenience for the observer. The antiglare property differs from the conventional “antiglare property”, which is a condition with complete absence of unwanted reflection of observers and backgrounds, and total halation and obscurity.

VG: Evaluation of “satisfactory” by at least 10 individuals.

G: Evaluation of “satisfactory” by at least 5-9 individuals.

P: Evaluation of “satisfactory” by 4 or fewer individuals.

(3) Blackness in dark surroundings: The liquid crystal television was set in a room in an environment with an illuminance of no greater than 5 Lx, a black screen was displayed, and the image was viewed by 15 subjects from a location about 1.5-2.0 m distant from the liquid crystal television, at different vertical and horizontal angles, for sensation evaluation of the following properties. The black screen was displayed on the screen of an externally connected laptop computer (Sony VAIO), with the entire background color set to “black”. The evaluation levels were as follows. Black display in dark surroundings was judged by whether or not gray was present and black could be seen without the impression of opalescence.

VG: Evaluation of “satisfactory” by at least 13 individuals.

G: Evaluation of “satisfactory” by at least 10-12 individuals.

F: Evaluation of “satisfactory” by 5-9 individuals.

P: Evaluation of “satisfactory” by 4 or fewer individuals.

(4) Black tightness: The liquid crystal television was again situated in a room with an environment at an illuminance of about 1,000 Lx and evaluated for blackness during power-off and blackness (black images) during power-on, as viewed directly from the front. The result was expressed as the degree of blackness.

VG: Evaluation of “satisfactory” by at least 13 individuals.

G: Evaluation of “satisfactory” by at least 10-12 individuals.

F: Evaluation of “satisfactory” by 5-9 individuals.

P: Evaluation of “satisfactory” by 4 or fewer individuals.

(5) Glazed black feel: A test material comprising an antiglare sheet attached to a black acrylic board using a transparent pressure-sensitive adhesive film for an optical film, was placed on a horizontal plane in a room with an environment at an illuminance of about 1,000 Lx and a visual sense evaluation was conducted by 15 viewers from the regular reflection direction on a 45 degree-incident plane with the triple wavelength tube lit, judging whether or not glazed black could be reproduced.

VG: Evaluation of “satisfactory” by at least 13 individuals.

G: Evaluation of “satisfactory” by at least 10-12 individuals.

F: Evaluation of “satisfactory” by 5-9 individuals.

P: Evaluation of “satisfactory” by 4 or fewer individuals.

The evaluation results for the antiglare sheets obtained in the examples and comparative examples are shown in Table 2.

As shown in Table 2, the antiglare sheets of the examples satisfied the ranges of the invention for Q/U and Log₁₀(Q₃₀/Q), and therefore had excellent image evaluations.

INDUSTRIAL APPLICABILITY

The antiglare sheet of the invention has excellent blackness in dark surroundings and vivid complexion and blackness, and can produce an image display device with an excellent antiglare property for dynamic images.

EXPLANATION OF SYMBOLS

-   1. 7. Antiglare sheets -   2. 8. Antiglare layers -   3-1. Diffusion particle -   3-2. Binder fine particle -   4. Binder resin -   5. 9. 11. Transparent base materials -   6. 12. Polarizing plates -   10. Polarized light layer -   13. Glass panel -   14. Color filter -   15. Transparent electrode -   16. Liquid crystal cell -   17. Backlight -   18. Glass panel (front panel) -   19. Display electrode (transparent electrode+path electrode) -   20. Transparent dielectric layer -   21. MgO -   22. Dielectric layer -   23. Glass panel (back plate) -   24. Address electrode -   25. Fluorescent material -   26. Plasma display panel (PDP) -   27. Front filter -   28. Spacer -   29. Enclosure -   30. Screw -   31. Front (display surface) 

The invention claimed is:
 1. An antiglare sheet having an antiglare layer comprising a binder resin, diffusion particles and binder fine particles on at least one side of a transparent base material, the antiglare layer having irregularities on the side opposite the transparent base material, the irregularities being formed by raised sections constituted by the diffusion particles and/or aggregates of the diffusion particles, the diffusion particles being surrounded by a localization layer with high density of the binder fine particles, and the binder fine particles being hydrophobic-treated fumed silica and/or a laminar inorganic compound, wherein the following inequalities (1) and (2) are satisfied to improve blackness in dark surroundings, to improve vivid complexion and blackness, and to prevent an increase of reflection thereby preventing the generation of stray light, 10<Q/U<36  (1) Log₁₀(Q ₃₀ /Q)<−6  (2) wherein Q is a transmission intensity in the direction of regular transmission, when visible light rays have been irradiated on the antiglare sheet perpendicular to the transparent base material side, wherein Q₃₀ is the transmission intensity in a direction 30 degrees from the direction of regular transmission, and wherein U is the mean value of the transmission intensity determined by extrapolation of a straight line connecting the transmission intensity in the direction +2 degrees from the direction of regular transmission with the transmission intensity in the direction +1 degree from the direction of regular transmission, and a straight line connecting the transmission intensity in the direction −2 degrees from the direction of regular transmission with the transmission intensity in the direction −1 degree from the direction of regular transmission, to regular transmission respectively.
 2. The antiglare sheet according to claim 1, wherein the specific gravity of the binder fine particles is greater than the specific gravity of the binder resin.
 3. The antiglare sheet according to claim 1, where the following inequality (3) is satisfied, 3<T<10  (3) wherein T (μm) is the thickness of the antiglare layer.
 4. The antiglare sheet according to claim 1, where the following inequality (4) is satisfied, Log₁₀(Q ₂₀ /Q)<−5.5  (4) wherein Q is the transmission intensity in the direction of regular transmission, when visible light rays are irradiated perpendicular to the antiglare sheet from the transparent base material side, and wherein Q₂₀ is the transmission intensity in the direction 20 degrees from the direction of regular transmission, when visible light rays are irradiated perpendicular to the antiglare sheet from the transparent base material side.
 5. The antiglare sheet according to claim 1, where the following inequality (5) is satisfied, 0≦Ha−Hi≦1.3  (5) wherein Ha (%) is the total haze value of the antiglare sheet and Hi (%) is the internal haze value of the antiglare sheet.
 6. The antiglare sheet according to claim 1, having a low refractive index layer formed on the uppermost surface layer.
 7. A polarizing plate employing the antiglare sheet according to claim
 1. 8. An image display device employing the polarizing plate according to claim
 7. 9. An image display device employing the antiglare sheet according to claim
 1. 10. A method for producing an antiglare sheet comprising a step of providing an antiglare layer comprising a binder resin, diffusion particles and binder fine particles on at least one side of a transparent base material, wherein the antiglare layer has irregularities on the side opposite the transparent base material, the irregularities are formed by raised sections constituted by the diffusion particles and/or aggregates of the diffusion particles, the diffusion particles are surrounded by a localization layer with high density of the binder fine particles, and the binder fine particles are hydrophobic-treated fumed silica and/or a laminar inorganic compound, wherein the antiglare sheet is adjusted so as to satisfy the following inequalities (1) and (2) to improve blackness in dark surroundings, to improve vivid complexion and blackness, and to prevent an increase of reflection thereby preventing the generation of stray light, 10<Q/U<36  (1) Log₁₀(Q ₃₀ /Q)<−6  (2) wherein Q is the transmission intensity in the direction of regular transmission, when visible light rays have been irradiated on the antiglare sheet perpendicular to the transparent base material side, wherein Q₃₀ is the transmission intensity in a direction 30 degrees from regular transmission, and wherein U is the mean value of the transmission intensity determined by extrapolation of a straight line connecting the transmission intensity in the direction +2 degrees from the direction of regular transmission with the transmission intensity in the direction +1 degree from the direction of regular transmission, and a straight line connecting the transmission intensity in the direction −2 degrees from the direction of regular transmission with the transmission intensity in the direction −1 degree from the direction of regular transmission, to regular transmission.
 11. A method for improving the vivid complexion and blackness, blackness in dark surroundings, antiglare property for dynamic images, glazed black feel and black tightness of an image device, wherein the image device has on the viewing side of the image display device an antiglare sheet having an antiglare layer comprising a binder resin, diffusion particles and binder fine particles on at least one side of a transparent base material, the antiglare layer having irregularities on the side opposite the transparent base material, the irregularities being formed by raised sections based on the diffusion particles and/or aggregates of the diffusion particles, the diffusion particles being surrounded by a localization layer with high density of the binder fine particles, and the binder fine particles being hydrophobic-treated fumed silica and/or a laminar inorganic compound, wherein the method comprises a step of controlling the transmission intensities of the antiglare sheet so as to satisfy the following inequalities (1) and (2) to improve blackness in dark surroundings, to improve vivid complexion and blackness, and to prevent an increase of reflection thereby preventing the generation of stray light, 10<Q/U<36  (1) Log₁₀(Q ₃₀ /Q)<−6  (2) wherein Q is the transmission intensity in the direction of regular transmission, when visible light rays have been irradiated on the antiglare sheet perpendicular to the transparent base material side, wherein Q₃₀ is the transmission intensity in a direction 30 degrees from the direction of regular transmission, and wherein U is the mean value of the transmission intensity determined by extrapolation of a straight line connecting the transmission intensity in the direction +2 degrees from the direction of regular transmission with the transmission intensity in the direction +1 degree from the direction of regular transmission, and a straight line connecting the transmission intensity in the direction −2 degrees from the direction of regular transmission with the transmission intensity in the direction −1 degree from the direction of regular transmission, to regular transmission.
 12. The method according to claim 11, wherein the specific gravity of the binder fine particles is greater than the specific gravity of the binder resin.
 13. The method according to claim 11, where the following inequality (3) is satisfied, 3<T<10  (3) wherein T (μm) is the thickness of the antiglare layer.
 14. The method according to claim 11, wherein the transmission intensities of the antiglare sheet is controlled so as to satisfy the following inequality (4), Log₁₀(Q ₂₀ /Q)<−5.5  (4) wherein Q is the transmission intensity in the direction of regular transmission, when visible light rays are irradiated perpendicular to the antiglare sheet from the transparent base material side, and wherein Q₂₀ is the transmission intensity in the direction 20 degrees from the direction of regular transmission, when visible light rays are irradiated perpendicular to the antiglare sheet from the transparent base material side.
 15. The method according to claim 11, where the following inequality (5) is satisfied, 0≦Ha−Hi≦1.3  (5) wherein Ha (%) is the total haze value of the antiglare sheet and Hi (%) is the internal haze value of the antiglare sheet.
 16. The method according to claim 11, wherein a low refractive index layer is formed on the uppermost surface layer of the antiglare sheet. 